1. Field of the Invention
This invention relates in general to color photography and in particular to new and improved color developing compositions and processes for forming photographic color images. More specifically, this invention relates to color development with a color developing composition, containing a primary aromatic amino color developing agent and an hydroxylamine, which is stabilized by the presence of a combination of sequestering agents.
2. Description of the Prior Art
The formation of color photographic images by the image-wise coupling of oxidized primary aromatic amino developing agents with color forming or coupling compounds to form indoaniline, indophenol, and azomethine dyes is well known. In these processes, the subtractive process of color formation is ordinarily used and the image dyes customarily formed are cyan, magenta, and yellow, the colors that are complementary to the primary colors, red, green, and blue, respectively. Usually phenol or naphthol couplers are used to form the cyan dye image; pyrazolone or cyanoacetyl derivative couplers are used to form the magenta dye image; and acylacetamide couplers are used to form the yellow dye image.
In these color photographic systems, the color forming coupler may be either in the developer solution or incorporated in the light-sensitive photograhic emulsion layer so that, during development, it is available in the emulsion layer to reach with the color developing agent that is oxidized by silver image development. Diffusible couplers are used in color developer solutions. Nondiffusing couplers are incorporated in photographic emulsion layers. When the dye image formed is to be used in situ, couplers are selected which form non-diffusing dyes. For image transfer color processes, couplers are used which will produce diffusible dyes capable of being mordanted or fixed in the receiving sheet.
In addition to a primary aromatic amino color developing agent, photographic color developing composition frequently contain hydroxylamine or a salt thereof which functions to protect the developing agent against aerial oxidation. They also generally contain a sequestering agent to stabilize the composition against the formation of precipitates and against undesired decomposition reactions, such as the decomposition of the hydroxylamine to generate ammonia. A variety of sequestering agents or combinations of sequestering agents have been proposed in the past for use in stabilizing photographic color developing compositions containing a primary aromatic amino color developing agent and an hydroxylamine. For example, sequestering agents described as being useful for this purpose include the 1,3-diamino-2-propanol tetraacetic acid of U.S. Pat. No. 2,875,049; the diethylenetriamine pentaacetic acid of U.S. Pat. No. 3,462,269; and combination of an aminopolycarboxylic acid and an aromatic polyhydroxy compound of U.S. Pat. No. 3,746,544; the combination of an amino-N,N-dimethylenephosphonic acid and a diphosphonic acid described in Research Disclosure, Volume 134, Item 13410, June 1975; the combination of an hydroxyalkylidene diphosphonic acid and an aminopolycarboxylic acid or of an hydroxyalkylidenediphosphonic acid and an aminopolyphosphonic acid of U.S. Pat. No. 3,994,730; the organic compounds having at least one phosphono group and at least one carboxy group in the molecule described in U.S. Pat. No. 4,083,723; and the combination of an aminophosphonic acid and an aminocarboxylic acid described in Research Disclosure, Volume 170, Item 17048, June 1978. However, in many cases the sequestering agents or sequestering agent combinations proposed in the prior art provide less than satisfactory results in respect to one or both of the aspects of avoiding precipitate formation and avoiding decomposition reactions. This is particularly the case under severe conditions when heavy metals, such as iron, which act to catalyze the decomposition of the hydroxylamine are present in the developer composition in substantial quantities.
It is toward the objective of providing a photographic color developing composition which has excellent stability in respect to both avoiding undesired precipitates and avoiding the harmful effects of decomposition that the present invention is directed.